So i recently was given one of those ford two seater 12v trucks and right away went to push it to 18v. I did this the same way i have for the last two power wheels by running a 12volt 12ah battery in series with a 6volt 12 ah battery. Using the existing wiring in the machine but i did put a terminal panel under the hood (rated at 30amps and up to 600volts) so that i could clean up the wiring. All new wires were 12gauge twisted pair with proper ends. Now the thing moves just like it should for an 18v and does well for about 20 minutes of full throttle then it starts to wind to a crawl within minutes after slowing. I hooked them up to my smart charger and both registered almost %50 charge left and both batteries were within %4 of each other so i know its not a matter of one batter crapping out before the other. Now the caveat here is both my kids were on it, one 7yr old girl and the other a skinny 5 year old boy. Either way i cant understand how it runs so well with hardly any over heating at all then a short time later starts the "low battery death crawl" but with still half a charge to go. Could it be a voltage issues some how? im totaly lost here so any input or suggestions would be very very appreciated. Thanks in advance!

So i recently was given one of those ford two seater 12v trucks and right away went to push it to 18v. I did this the same way i have for the last two power wheels by running a 12volt 12ah battery in series with a 6volt 12 ah battery. Using the existing wiring in the machine but i did put a terminal panel under the hood (rated at 30amps and up to 600volts) so that i could clean up the wiring. All new wires were 12gauge twisted pair with proper ends. Now the thing moves just like it should for an 18v and does well for about 20 minutes of full throttle then it starts to wind to a crawl within minutes after slowing. I hooked them up to my smart charger and both registered almost %50 charge left and both batteries were within %4 of each other so i know its not a matter of one batter crapping out before the other. Now the caveat here is both my kids were on it, one 7yr old girl and the other a skinny 5 year old boy. Either way i cant understand how it runs so well with hardly any over heating at all then a short time later starts the "low battery death crawl" but with still half a charge to go. Could it be a voltage issues some how? im totaly lost here so any input or suggestions would be very very appreciated. Thanks in advance!

its not so much that i mind the shorter ride time its more that when the machine started to limp along like the batteries were almost fully depleted it was actually that they both had right at %50 charge left. This was per a smart charter i have that shows the remaining percentage of charge on a battery. Its been accurate so far so i am still in the dark on why the machine would slow down like it was almost out of juice when the batteries were only half depleted. If thats normal then i can live with that but i just dont see why it would behave like this. Thanks for the help

It does sound like one battery is weaker than the other. 50% is just the little amber light on your smart charger right? After 20 minutes one battery is probably dead and the other battery then has to take the entire load (including the dead battery). You are going to be very lucky to have two batteries that have the exact same amp draw when running them in series. You would need to measure the voltage of each battery while under a load to determine which one was the weaker of the two (most notable when they are drained down and the truck is moving slowly).